The present invention relates to the field of pumping of oil well fluids from a downhole location in an oil well to the surface adjacent the well. More particularly, the invention relates to the protection of the pump from well bore solids that can abrade or jam the pump. More particularly still, the invention relates to the filtration of solids from the well bore fluid by filter media prior to the entry of the fluids into the pump, and the downhole cleaning of the filter media to limit the need to remove the pump and filter from the well bore to replace or clean the filter after the filter has restrained amounts of the solid particulates sufficient to reduce its capacity.
Downhole pumps are placed in well bores to pump well fluids from a location within the well bore upward to the surface. Such pumps provide the energy to lift the well fluid where the natural well pressure is too low to force the well fluid to the surface. One major consideration in the cost of producing oil from low production wells is the cost of lifting the well fluid to the surface. The lifting cost is a function of original equipment cost and the cost to run, and maintain or replace the equipment, and the cost to service the well and equipment. Pumping costs are a major contributor to production costs, and marginally producing wells are commonly abandoned because the overall cost of pumping, including equipment maintenance, is too high in comparison to the value of any oil produced from the well. This is particularly true where the well is pumping from a formation which gives up produced fluid with a high abrasive particulate content. These abrasives tend to migrate with the well fluid into the pump, and contribute to high pump wear and maintenance. As a result of the presence of these particulates, rapid abrasive damage can occur on the precision pump surfaces, particularly on the critical interface of the plunger with the barrel. Additionally, many other pump components, such as critical valves, abrade in the presence of the particulates, which leads to inadequate pump performance. As a result of this wear and damage, the pump must be pulled out of the well to be repaired or replaced. Removal and reinsertion of the pump may take several hours, or several days, at significant cost to the well operator. The more abrasive the well fluid, the more often the pump must be pulled for servicing and repair.
U.S. Pat. No. 4,969,518, Schmitt, et al., fully incorporated herein by reference, discloses a significant improvement in pump structure that permits a significant increase in pump downhole time, i.e., the length of time the pump remains in the hole pumping, before it must be removed for service. This improvement is provided by a filter member having tortuous paths therein that decrease in size from the well side to the pump side of the filter. Additionally, the filter includes a trip member that allows fluid to bypass the filter if the filter should become clogged while still in service. This filter provides substantial protection to the pump, and permits the pump to remain in the well bore for longer periods without service or replacement, and thus lowers the cost of pump maintenance, repair or replacement.
Despite the technological advance of the invention described in U.S. Pat. No. 4,969,518, there was still a need to pull the pump after the filter media capacity is reduced by becoming clogged, or loaded. For example, on a well in Wyoming with a history of requiring pump repair every 7 days, the filter media of the '518 patent increased the pump downhole time to 214 days. However, despite the tremendous decrease in lift cost associated with such an increase in downhole time, the pump still has to be removed for filter replacement and pump inspection/service.
The invention of my copending application Ser. No. 08/100,612, filed Jul. 30, 1993, now U.S. Pat. No. 5,413,721, the disclosure of which is incorporated herein by reference, provided a significant improvement over the '518 invention. That invention provided a downhole cleaner which, in cooperation with the pump, forces well bore particulates outwardly from the filter upon a preselected reduction in filter efficiency exhibited by a preselected pressure differential across the filter media of the filter, which cleans the filter in place in the well bore and permits continued use of the filter and pump without the need to pull the pump to clean or replace the filter.
In this invention, however, in some installations it was necessary or desirable to stop the sucker rod pump after the filter was cleaned for long enough to make sure that particles forced from the filter had time to settle to the bottom of the well bore and thereby avoid starting flow of well bore fluids which still contained a high proportion of particulate matter. This required the presence of an operator at the surface to turn the pump off and on or the use of special surface equipment to automatically delay the initiation of pumping operations.